In order to maintain required precision, the optical system (optical apparatus) of a projection type image display apparatus such as a liquid crystal projector is generally encased in a heat-resistive resin casing that does not exhibit appreciable heat-shrinkage, since the light source of the image display apparatus becomes very hot.
In spite the elements of the optical system must be firmly fixed at precise positions, they have dimensional tolerances. However, heat-resistive non-shrinkable resins generally have little elasticity, so that they can scarcely absorb the dimensional tolerances of the optical elements. As a consequence, each of the optical elements is mostly fixed using an additional resilient element, as disclosed in Japanese Patent Application Laid Open No. 2003-287814.
This approach, however, requires a large number of such additional resilient elements, which disadvantageously adds extra manufacturing steps and cost to the apparatus, in addition to the cost of the heat-resistive resin.